1. Field of the Invention
The field of this invention relates to a process for upgrading sulfer-containing petroleum asphaltenes.
2. The Prior Art
High sulfur petroleum asphaltenes are not a desirable fuel and are not a desirable feedstock for producing other petroleum products.
Heretofore, low sulfur petroleum asphaltenes have been obtained by employing low sulfur crude oils or hydrodesulfurized feedstocks. Low sulfur crude oils, however, are expensive and are becoming increasingly less available, especially in North America. Hydrodesulfurization is also expensive because it is capital intensive and consumes valuable hydrogen.
Heretofore, it has been proposed to use water heated to supercritical temperature and pressure in a process to shatter coal in a manner such that coal particles and mineral matter particles can be separated. For example, U.S. Pat. No. 4,313,737 to Massey, et al. discloses a process for treating coal, oil shale or other porous, fluid-permeable, friable hydrocarbonaceous solid containing an admixture of hydrocarbonaceous particles and mineral matter particles with water heated to supercritical temperature and pressure and then rapidly reducing the pressure to shatter the friable hydrocarbonaceous solid containing mineral matter in a manner such the mineral matter can be separated from the hydrocarbonaceous material. Separating the mineral matter from the hydrocarbonaceous mineral can reduce the sulfur content of the hydrocarbonaceous matter because sulfur is often associated with the mineral matter.
High sulfur petroleum asphaltenes are not hydrocarbonaceous material containing mineral matter such as disclosed in the process of the above patent as being amenable to beneficiation in the process described. Rather, asphaltenes are non-pourous dark brown to black friable solids that have no definite melting point, and when heated, usually intumesce, then decompose leaving a carbonaceous residue. They can be obtained from petroleums and bitumens by addition of a nonpolar solvent (such as a hydrocarbon) with a surface tension lower than 25 dynes cm.sup.-1 at 25.degree. C. (such as liquefied petroleum gases, the low-boiling petroleum naphthas, petroleum ether, pentane, isopentane, and hexane) but are soluble in liquids having a surface tension above 25 dynes cm.sup.-1 (such as pyridine, carbon disulfide, carbon tetrachloride, and benzene).
Asphaltenes have been characterized in a variety of ways, see, for example, "Chemistry of Asphaltenes", Advances in Chemistry Series, No. 195, Burger & Li, Copyright 1981 by the American Chemical Society, incorporated herein by reference.
It now has been surprisingly found that high sulfur petroleum asphaltenes can be treated with a fluid comprising water, methanol, carbon dioxide and mixtures thereof, at supercritical temperatures and pressures in order to reduce or eliminate sulfur associated with petroleum asphaltenes. The sulfur reduction that occurs is not due to size reduction, but rather is apparently due to chemical reactions which occur at these conditions.
Since prior art processes for obtaining low sulfur petroleum asphaltenes are becoming increasingly less desirable, this discovery can be quite useful since it portends new more desirable processes for obtaining low sulfur petroleum asphaltenes.